[chiphead]

Lets use my example for the K&N calculator

407 cubic inches at 5700 RPM.

I get 111 square inches of filter area required.

With a 14" diameter element, that gives a required height of 3.27 inches.

I'm currently running a 14" diameter, 3.5" tall element with a (I think) 1/2" drop base.

A google search says the top of the vent on a QF 4150 is 2" above the filter mounting surface.

So 3.5" filter minus 1/2 drop gives 3". Subtract 2" for the vent height, and I should have about 1" between the top of the vent stacks and the inside of the air cleaner lid. (neglecting the slight dome shape of the lid.)

My other filter is a 3". The math shows that the 3" filter would put the lid about 1/2" away from the vents. I would verify the AFR with a meter to see if that impacts the carb metering, before I called that good to go. That's what I plan on doing, since I have to use the 3" filter to fit a 1/2" spacer under the 4150, so I don't hit the GTO hood. The math looks like a 3" filter would be marginal filter area in my application. Not sure how VE or arbitrary RPM chosen affects the filter sizing. My calculated requirements are likely a little overkill. Something to ponder.

I do know that the 3" filter and a 3/4"-1" drop base made the engine go into the 9.x for AFR at WOT. Rich piggy. I assume this was due to vent clearance and not an issue with the carb.